The overall goals of this new Program Project are to develop a comprehensive structural, mechanistic, functional and clinical understanding of HDL biology and its relationship to atherosclerotic heart disease. The Program is comprised of 3 focused and interrelated Projects that focus on the common theme of investigating various aspects of HDL pathobiology, including asking fundamental questions about HDL particle genesis, maturation, remodeling, structure/function, clinical relevance and use in both novel diagnostic and therapeutic interventions. Each Project also explores the potential biological consequences of HDL alterations in structure and function by specific oxidative modifications that occur within atherosclerotic plaque. Experimental studies proposed in each of the three Projects rely upon collaborative interactions with each of the other Projects. Project 1 explores fundamental questions about the structure of nascent and mature forms of HDL, its complexes with proteins involved in HDL maturation (LCAT) and cholesterol delivery to the liver and steroidogenic tissues (SRB1), as well as oxidative modifications to HDL in human plasma and atherosclerotic plaque that adversely impact upon the many biological functions of the particle. Project 2 explores the role of various participants in the RCT processes in atherosclerotic plaque regression, and the role of both HDL, and specific oxidized forms of HDL, in modulating macrophage phenotype and egress within the vessel wall during atherosclerotic plaque regression. Project 3 studies mechanisms through which ABCA1 interacts with apoA1 during HDL biogenesis, specific structural features critical to this process, and the potential utility of oxidant resistant forms of apoA1 as a therapeutic for promoting atherosclerosis plaque regression. Three scientific cores (Mass Spectrometry and Biophysics; Regression of Atherosclerosis; and Recombinant Protein Expression and Molecular Cloning) and an Administrative Core provide multi-project support, expertise and service in a cost-effective manner, significantly strengthening the entire research program. The proposed Program Project will yield greater understanding of structural features of HDL and HDL-associated protein complexes critical to cholesterol homeostasis, reverse cholesterol transport, and atherosclerotic plaque progression/regression. It also will identify the functional and clinicai impact of site-specific oxidative modifications to HDL that occur within human atheroma. Finally, it may also lead to new diagnostic and therapeutic approaches toward cardiovascular risk assessment and therapy. The overall goals of this Program Project are to develop a comprehensive structural, mechanistic, functional and clinical understanding of HDL biology and its relationship to atherosclerotic heart disease. Each ofthe Projects explores both normal functions of HDL in cholesterol homeostasis and plaque regression, as well as in vivo functional consequences of HDL alterations in structure by specific oxidative modifications that occur within human atheroma. New diagnostic and therapeutic interventions are a major focus of investigation.